Theoretical investigation of fundamental inherent physical and optoelectronic properties of ZnSnSb2 chalcopyrite semiconductor

Abstract

Here in, we have investigated fundamental inherent physical properties like as structural, electronic, optical, elastic, thermal etc of the ZnSnSb2 by using the accurate full potential linearized augmented plane wave (FP-LAPW) method. These materials have higher energy gaps and lower melting points as compared to their binary analogues, because of which they are considered to be important in crystal growth studies and device applications. For structural properties, the minimization has been done in two steps, first parameter u is minimized by the calculation of the internal forces acting on the atoms within the unit cell until the forces become negligible, for this MINI task is used, which is included in the WIEN2K code. Second, the total energy of crystal is calculated for a grid of volume of the unit cell (V) and c/a values. Five values of c/a are used for each volume and a polynomial is fitted to the calculated energies to calculate the best c/a ratio. We have presented the electronic and optical properties with the recently developed density functional of Tran and Blaha. Furthermore, optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients, optical conductivities, were calculated for photon energies up to 40 eV. We have used WC and TB-mBJ exchange correlation potential for these properties and yield a direct band gap of 0.46 eV for this material and the obtained electronic band gap matches well with the experimental data. The TB-mBJ potential gives results in good agreement with experimental values that are similar to those produced by more sophisticated methods, but at much lower computational costs. The main peaks of real part of the electronic dielectric function ε1(ω) which is mainly generated by electronic transition from the top of the valence band to the bottom of conduction band, occurs at 1.59 eV and ε1(ω) spectra further decreases up to 4.99 eV. The imaginary part of the electronic dielectric constant ε2(ω) is the fundamental factor of the optical properties of a material. The proposed study shows that the critical point of the ε2(ω) occurs at 0.42 eV, which is closely related to the obtained band gap value 0.46 eV. The maximum reflectivity occurs in region 3.74-11.33 eV. This material has non-vanishing conductivity in the visible light region (1.65 eV-3.1 eV), the main peak occurs at 3.80 eV, which fall in the UV region. The elastic constants at equilibrium in BCT structure have also determined. The elastic stiffness tensor of chalcopyrite compounds has six independent components, because of the symmetry properties of the space group, namely C11, C12, C13, C33, C44 and C66 in Young notation. The thermal properties such as thermal expansion, heat capacity, Debye temperature, entropy, Grüneisen parameter and bulk modulus were calculated employing the quasi-harmonic Debye model at different temperatures and pressures and the silent results were interpreted. To determine the thermodynamic properties through the quasi-harmonic Debye model, a temperature range 0 K 500 K has been taken. The pressure effects are studied in the 0–7 GPa range. Similar trends have been observed in the considered temperature range, but above 600 K trends get disturbed which may be due to melting of material. Based on the semi-empirical relation, we have determined the hardness of the materials, which attributed to different covalent bonding strengths. Most of the investigated parameters are reported for the first time.